(1) Field of the Invention
The invention relates to a process for dry etching multilayer structures, and more particularly, to a process for dry etching a multilayer tungsten silicide polysilicon gate structure in the manufacture of integrated circuits.
(2) Description of the Prior Art
Dry etching, as defined by Thomas et al in his U.S. Pat. No. 4,680,086, is process in which a gas or a plasma containing at least one reactive specie and which is energized by a radio frequency when placed in contact with a structure to be etched, causes a reaction at the surface of the metal wherein the reacted material is removed in the form of a gas. A common problem with dry etching is the undercutting of the polysilicon gate layer.
For example, U.S. Pat. Nos. 4,680,086 to Thomas et al, 4,786,360 to Cote et al, 4,948,462 to Rossen, and 4,844,767 to Okudaira et al describe the use of various chlorine and fluorine gases to etch the polysilicon gate layer, especially tungsten, to prevent the undercutting problem. U.S. Pat. No. 4,980,018 to Mu et al uses chlorine and helium gases to pattern tungsten after using forms of fluorine and chlorine gases. The above cited US Patent to Okudaira et al mentions the protective sidewall coating that develops during etching to protect against undercutting. Sidewall passivation effect during etching is described by S. M. Sze in his book, VLSI Technology, Second Edition, McGraw-Hill International Editions, New York, NY c.1988, p.200.